Reducing agent injection device and exhaust gas treatment method

ABSTRACT

A reducing agent injection device includes a first honeycomb structure and a urea spraying device spraying a urea water solution in mist form. A pair of electrode members is formed in the first honeycomb structure. The ratio L/D of length L in the cell extending direction of the honeycomb structure body to diameter D of the cross section perpendicular to the cell extending direction is 0.5 to 1.2. Also, it is preferable that a urea hydrolysis catalyzer is provided in the second end face side of the honeycomb structure body, with a gap from the second end face.

The present application is an application based on JP-2016-068902 filedon Mar. 30, 2016 with Japan Patent Office, the entire contents of whichare incorporated herein by reference.

BACKGROUND OF THE INVENTION Field of the Invention

The present invention relates to a reducing agent injection device forpurifying exhaust gas, and an exhaust gas treatment device.

Description of the Related Art

Conventionally, a selective catalytic reduction type NO_(X) catalyst (anSCR catalyst) has been used to purify nitrogen oxides (NO_(X)) in theexhaust gas discharged from various kinds of engines and the like (forexample, see Patent Document 1).

The exhaust gas purifying device described in Patent Document 1 has acatalyst (an SCR catalyst) mounted on an exhaust pipe of an engine andmeans for injecting urea water into the exhaust pipe between the engineand the catalyst. Moreover, a plurality of urea water injection means,which mixes the urea water and the exhaust gas, and mixes the urea waterwith the exhaust gas while causing the urea water to react with aspecific component in the exhaust gas by the catalyst, are provided in aplurality of places.

Because the exhaust gas purifying device described in Patent Document 1decomposes the urea water by heat of the exhaust gas (necessary to be200° C. or more), there has been a problem that urea is less likely toreact when the temperature of the exhaust gas lowers due to improvementof fuel consumption of the engine and the like.

Therefore, an exhaust gas treatment device that promotes a decompositionof urea to NH₃, by adding urea to an electrically heated honeycombstructure (honeycomb heater) has been suggested (Patent Document 2).NO_(X) purification becomes possible also in the low temperature regionof the exhaust gas by adding to a pipe as NH₃ gas.

[Patent Document 1] JP-A-2007-327377

[Patent Document 2] WO 2014/148506

SUMMARY OF THE INVENTION

However, when urea is added to an electrically heated honeycombstructure (honeycomb heater), the temperature of a portion to which ureais added is lowered, and temperature unevenness in the honeycomb heateroccurs. Therefore, there has been a concern that urea deposit (deposit:crystal caused by urea) is formed at a low-temperature section. Whenurea deposit is generated, the path of the honeycomb heater is cut, anddecomposition of urea to NH₃ is inhibited, thus it leads to a functionalloss.

Urea deposit tends to depend on the temperature of the honeycomb heaterwhen urea is added, thus increase in energizing power is effective forsuppressing urea deposit. However, when the amount of urea added isincreased, the temperature of the honeycomb heater is further lowered,and high electric power is necessary, thus the temperature distributionin the honeycomb heater also becomes larger, and it leads to breakage ofthe honeycomb heater.

An object of the present invention is to provide a reducing agentinjection device that can suppress urea deposit, in an exhaust gastreatment device that promotes decomposition of urea to NH₃, by addingurea to an electrically heated honeycomb structure (honeycomb heater),and an exhaust gas treatment device provided therewith.

In order to solve the above problem, according to the present invention,the following reducing agent injection device, and exhaust gas treatmentdevice are provided.

[1] A reducing agent injection device, including: a first honeycombstructure that has a pillar-shaped honeycomb structure body havingpartition walls defining and forming a plurality of cells which isthrough channels of a fluid and extends from a first end face being anend face on an inflow side of the fluid to a second end face being anend face on an outflow side of the fluid, and that has at least a pairof electrode members arranged in a side surface of the honeycombstructure body; and a urea spraying device that sprays a urea watersolution in mist form, wherein each of the pair of electrode members isformed in a band shape extending to a cell extending direction of thehoneycomb structure body, and one electrode member of the pair ofelectrode members is arranged on an opposite side of the other electrodemember of the pair of electrode members with respect to a center of thehoneycomb structure body sandwiched by the pair of electrode members, ina cross section perpendicular to the cell extending direction, the ratioL/D of length L in the cell extending direction of the honeycombstructure body to diameter D of the cross section perpendicular to thecell extending direction is 0.5 to 1.2, and the urea water solutionsprayed from the urea spraying device is supplied into the cells fromthe first end face of the honeycomb structure body, and urea in the ureawater solution supplied into the cells is heated and hydrolyzed in theelectrically heated honeycomb structure body to generate ammonia, andthe ammonia is discharged outside the honeycomb structure body from thesecond end face and is injected outside.

[2] The reducing agent injection device according to [1], wherein a ureahydrolysis catalyst is provided in the second end face side of thehoneycomb structure body, with a gap from the second end face.

[3] An exhaust gas treatment device, including: an exhaust pipe thatflows an exhaust gas containing NO_(X); the reducing agent injectiondevice according to [1] or [2] that injects ammonia into the exhaustpipe; and an SCR catalyst arranged on a downstream side of the exhaustpipe with respect to a position where the ammonia is injected.

According to the reducing agent injection device of the presentinvention, the urea water solution sprayed by the urea spraying deviceis supplied into the cell of the honeycomb structure. Then, the urea inthe urea water solution is heated and hydrolyzed in the electricallyheated honeycomb structure to generate ammonia, and the generatedammonia is injected. The ratio L/D of length L in the cell extendingdirection of the honeycomb structure body to diameter D of the crosssection perpendicular to the cell extending direction is 0.5 to 1.2,whereby it is easy to uniformly heat the honeycomb structure body, andhigh electric power is not required for heating. Therefore, thehoneycomb structure body does not break due to heat, and the sprayedurea water solution does not adhere as urea deposit (also simplyreferred to as deposit).

According to the exhaust gas treatment device of the present invention,because the reducing agent injection device of the present inventiondescribed above is included, ammonia can be generated from the ureawater solution with less energy even when the exhaust gas is at lowtemperature. Then, NO_(X) in the exhaust gas can be treated with lessenergy.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram showing a cross section of one embodimentof a reducing agent injection device of the present invention;

FIG. 2 is a plane view schematically showing an end face of a honeycombstructure constituting one embodiment of a reducing agent injectiondevice of the present invention; and

FIG. 3 is a schematic diagram showing a cross section of one embodimentof an exhaust gas treatment device of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Hereinbelow, the embodiments of the present invention are described inreference to the drawings. The present invention is not limited to thefollowing embodiments, and a change, modification and improvement may beadded without departing from the scope of the invention.

(1) Reducing Agent Injection Device:

FIG. 1 is a schematic diagram showing a cross section (cross sectionparallel to a cell 16 extending direction of a honeycomb structure body11) of one embodiment of a reducing agent injection device 100 of thepresent invention. As shown in FIG. 1, one embodiment of the reducingagent injection device 100 of the present invention includes thehoneycomb structure 1 (also referred to as first honeycomb structure, orhoneycomb heater) and a urea spraying device 2 spraying a urea watersolution in mist form. The first honeycomb structure 1 has apillar-shaped honeycomb structure body 11 and a pair of electrodemembers 12 and 12 arranged in a side surface of the honeycomb structurebody 11. The honeycomb structure body 11 has “partition walls 15defining and forming “a plurality of cells 16 which is through channelsof a fluid and extends from a first end face 13 being an end face on aninflow side of the fluid to a second end face 14 being an end face on anoutflow side of the fluid.”” Each of the pair of electrode members 12and 12 is formed in a band shape extending in the cell 16 extendingdirection of the honeycomb structure body 11. In a cross sectionperpendicular to the cell 16 extending direction, one electrode member12 of the pair of electrode members 12 and 12 is arranged on an oppositeside of the other electrode member 12 of the pair of electrode members12 and 12 sandwiching a center of the honeycomb structure body 11. Theelectrode member 12 is constituted by at least one pair, and may beconstituted by plural pairs for improving heat generating efficiency ofa heater. The ratio L/D of length L in the cell 16 extending directionof the honeycomb structure body 11 to diameter D of the cross sectionperpendicular to the cell 16 extending direction is 0.5 to 1.2.

The “diameter D” herein refers to a diameter of the honeycomb structure1 (containing a circumferential wall, not containing an electrodemember). When the shape of the cross section perpendicular to the cell16 extending direction of the honeycomb structure body 11 is not circle,the distance between facing circumferential walls passing through thecenter point is D. When the shape of the cross section is square, oneside is D, and when the shape of the cross section is ellipse orrectangle, the average of the lengths in the major axis direction andthe minor axis direction is D. The “length L” refers to a length in thecell 16 extending direction of the honeycomb structure 1, namely, a fulllength. The ratio L/D is preferably 0.5 to 1.2, more preferably 0.5 to1.0, and further preferably 0.7 to 0.9.

In the reducing agent injection device 100 of the embodiment, a ureawater solution a sprayed from the urea spraying device 2 is suppliedinto the cell 16 from the first end face 13 of the honeycomb structurebody 11. Then, urea in the urea water solution supplied into the cell 16is heated and hydrolyzed in the electrically heated honeycomb structurebody 11 to generate ammonia (reducing agent). Moreover, ammonia b isdischarged outside the honeycomb structure body 11 from the second endface 14.

When the ammonia b is discharged from the second end face 14 of theelectrically heated honeycomb structure body 11, isocyanic acid (HNCO)that is not generated as ammonia b may be discharged together.Therefore, it is preferable that a urea hydrolysis catalyst 40 isprovided in the second end face side of the honeycomb structure body 11,with a gap from the second end face 14. The urea hydrolysis catalyst 40is provided, whereby isocyanic acid can be converted to ammonia. Asshown in FIG. 1, the urea hydrolysis catalyst 40 is set away from thehoneycomb structure body 11. Therefore, even when the honeycombstructure body 11 is electrically heated, the catalyst is not affected,and is not lost.

In consequence, according to the reducing agent injection device 100 ofthe embodiment, the urea water solution a sprayed from the urea sprayingdevice 2 is supplied into the cell 16 of the first honeycomb structure1. Then, the urea in the urea water solution is heated and hydrolyzed inthe electrically heated first honeycomb structure 1 to generate ammonia.Moreover, the generated ammonia b is injected outside. Also, isocyanicacid that is not generated as ammonia b inside the first honeycombstructure 1 is generated as ammonia b with the urea hydrolysis catalyst40 arranged in the downstream of the first honeycomb structure 1, andinjected outside.

In the reducing agent injection device 100 of the embodiment, a rawmaterial for generation of ammonia is the urea water solution.Therefore, a urea water solution distributed on the market (for example,AdBlue (a urea water solution of 32.5% by mass: a registered trademarkof the German Automotive Industry Association (VDA)) can be used.Accordingly, it is also highly convenient in terms of procurement of aurea water solution as a raw material for generation of ammonia.

The ratio L/D of length L in the cell 16 extending direction of thehoneycomb structure body 11 to diameter D of the cross sectionperpendicular to the cell 16 extending direction is 0.5 to 1.2, wherebyit is easy to uniformly heat the honeycomb structure body 11, and highelectric power is not required for heating. Therefore, the honeycombstructure body 11 does not break due to heat, and the sprayed urea watersolution does not adhere as urea deposit.

In the reducing agent injection device 100 of the embodiment, the firsthoneycomb structure 1 and the urea hydrolysis catalyst 40 are housed ina tubular outer cylinder 4. The first honeycomb structure 1 and the ureahydrolysis catalyst 40 are secured inside the outer cylinder 4 by aninsulation supporting portion 5.

As shown in FIG. 2, in the first honeycomb structure 1, the shape of thefirst end face 13 of the honeycomb structure body 11 is preferablysquare. The shape of the first end face 13 is not limited to a squareshape, and may be a rectangular shape, other polygonal shape, a roundshape or an oval shape or the like. The shape of the first end face 13is the same as that of the second end face 14, and further preferablyalso the same as that of a cross section, which is perpendicular to thecell 16 extending direction of the honeycomb structure body 11.

In addition, a urea spraying space 3 is preferably formed between thefirst end face 13 of the honeycomb structure body 11 and the ureaspraying device 2. The urea spraying space 3 is a space formed by thefirst end face 13 of the first honeycomb structure 1, the urea sprayingdevice 2, and the outer cylinder 4. In the reducing agent injectiondevice 100 of the embodiment, when the urea spraying space 3 is formed,the urea water solution a sprayed from the urea spraying device 2 issupplied into the cell 16 from the first end face 13 of the honeycombstructure body 11 through the urea spraying space 3.

The outer cylinder 4 has a tubular shape having the inlet side endportion 21 as one end portion and the outlet side end portion 22 as theother end portion. At a distal end of the outlet side end portion 22,the injection port 23 as an open end for injection of the ammonia gas isformed. Inside the inlet side end portion 21 of the outer cylinder 4,the urea spraying device 2 is mounted. The material of the outercylinder 4 is preferably stainless steel and the like.

The first honeycomb structure 1 is secured (held) inside the outercylinder 4 by the insulation supporting portion 5. This ensuresinsulation between the first honeycomb structure 1 and the outercylinder 4. The material of the insulation supporting portion 5 ispreferably alumina. There may be a portion (space), where the insulationsupporting portion 5 is not arranged, between the first honeycombstructure 1 and the outer cylinder 4. Also, the whole outercircumference of the first honeycomb structure 1 may be covered by theinsulation supporting portion 5.

The reducing agent injection device 100 of the embodiment is configuredsuch that the ammonia discharged from the second end face 14 of thefirst honeycomb structure 1 is injected from the injection port 23through the inside of the outlet side end portion 22 of the outercylinder 4.

The following further describes the reducing agent injection device 100of the embodiment by respective constituent components.

(1-1) First Honeycomb Structure:

In the reducing agent injection device 100 of the embodiment, the firsthoneycomb structure 1 includes the honeycomb structure body 11 and thepair of electrode members 12 and 12, as described above. The firsthoneycomb structure 1 has partition walls 15 defining and forming “aplurality of cells 16 which is through channels of a fluid and extendsfrom a first end face 13 to a second end face 14”.

In the honeycomb structure body 11, a circumferential wall 17 isarranged outside the partition wall 15. In the honeycomb structure body11, the material of the partition wall 15 and the circumferential wall17 is preferably ceramic. Especially, the material of the partition wall15 and the circumferential wall 17 preferably contains a“silicon-silicon carbide composite material”, “silicon carbide” and thelike as a main component. Among these, the material further preferablycontains a “silicon-silicon carbide composite material” as a maincomponent. By using such materials, it becomes easier to adjustelectrical resistivity of the honeycomb structure body 11 to any valueby change of a ratio of silicon carbide to silicon. Here, thesilicon-silicon carbide composite material contains silicon carbideparticles as aggregates and metal silicon as a bonding material forbonding the silicon carbide particles. In the silicon-silicon carbidecomposite material, a plurality of silicon carbide particles ispreferably bonded by metal silicon. The above-described “siliconcarbide” is formed by the silicon carbide particles sintered together.The “main component” herein means the component occupying 90% by mass ormore.

The electrical resistivity of the honeycomb structure body 11 ispreferably from 0.01 Ωcm to 500 Ωcm, and is further preferably from 0.1Ωcm to 200 Ωcm. This allows causing the honeycomb structure 1 (honeycombstructure body 11) to effectively generate heat by application ofvoltage to the pair of electrode members 12 and 12. Especially, theabove-described electrical resistivity preferably causes the firsthoneycomb structure 1 (honeycomb structure body 11) to generate heat to160° C. to 600° C. by use of a power source with voltages of 12 V to 200V. The electrical resistivity of the honeycomb structure body 11 is avalue at 25° C. The electrical resistivity of the honeycomb structurebody 11 is the value measured by a four-terminal method.

In the honeycomb structure body 11, the surface area per unit volume ispreferably 5 cm²/cm³ or more, further preferably from 8 cm²/cm³ to 45cm²/cm³, and especially preferably from 20 cm²/cm³ to 40 cm²/cm³. Whenthe surface area per unit volume is smaller than 5 cm²/cm³, a contactarea with urea water becomes smaller, so that the treatment rate of theurea water solution, namely the generation amount (generation rate) ofammonia may decrease. The surface area of the honeycomb structure bodyis the area of the surface of the partition wall 15 of the honeycombstructure body 11.

In the first honeycomb structure 1 (honeycomb structure body 11), thethickness of the partition wall 15 is preferably from 0.06 mm to 1.5 mm,and further preferably from 0.10 mm to 0.80 mm. When the thickness ofthe partition wall 15 is thicker than 1.5 mm, the pressure loss becomeslarger, and the treatment rate of the urea water solution, namely thegeneration amount (generation rate) of ammonia may decrease. When thethickness of the partition wall 15 is thinner than 0.06 mm, it may bebroken by thermal shock by energization. When the shape of the cell 16(the shape perpendicular to the cell extending direction) is circle, thethickness of the partition wall means the thickness of the partitionwall for “a portion where the distance between the cells is shortest(the portion where the partition wall is thinnest).” The cell density ispreferably from 7 cells/cm² to 140 cells/cm², and further preferablyfrom 15 cells/cm² to 120 cells/cm². When the cell density is smallerthan 7 cells/cm², the contact area with urea water becomes smaller, sothat the treatment rate of the urea water solution, namely thegeneration amount (generation rate) of the ammonia may decrease. Whenthe cell density is larger than 140 cells/cm², the pressure loss becomeslarger, and the treatment rate of the urea water solution, namely thegeneration amount (generation rate) of ammonia may decrease.

The reducing agent injection device 100 of the present inventionpreferably has a plugging portion in “an end portion on the first endface 13 side of a part of the cells 16 of the honeycomb structure body42”. The material of the plugging portion is preferably the same as thematerial of the partition wall, and may be other material.

As to the size of the first honeycomb structure 1, the area of the firstend face 13 (the second end face 14) is preferably from 50 mm² to 10000mm², and further preferably 100 mm² to 8000 mm².

In the first honeycomb structure 1, the shape of the cells 16 in thecross section perpendicular to the cell 16 extending direction ispreferably a round shape, an oval shape, a quadrilateral shape, ahexagonal shape or an octagonal shape, or a combination of these shapes.Forming the shape of the cell in this way decreases the pressure losswhen flowing the exhaust gas in the honeycomb structure and makes itpossible to efficiently hydrolyze the urea. In the first honeycombstructure 1 shown in FIG. 2, the shape of the cells 16 in the crosssection (the first end face) perpendicular to the cell 16 extendingdirection is circle.

Each of the pair of electrode members 12 and 12 is formed in a bandshape extending in the cell 16 extending direction of the honeycombstructure body 11. Further, the electrode member 12 is preferably formedin a wider width expanding also in a circumferential direction of thehoneycomb structure body 11. In the cross section perpendicular to thecell 16 extending direction, one electrode member 12 is arranged in theopposite side with respect to the other electrode member 12 with acenter of the honeycomb structure body 11 sandwiched. This can reducedeviation of a current flowing inside the honeycomb structure body 11when a voltage is applied between the pair of electrode members 12 and12. Then, this can reduce variation of heat generation inside thehoneycomb structure body 11.

In the first honeycomb structure 1, the main component of the electrodemember 12 is preferably the same as the main component of the partitionwall 15 and the circumferential wall 17.

The electrical resistivity of the electrode member 12 is preferably from0.0001 Ωcm to 100 Ωcm, and further preferably from 0.001 Ωcm to 50 Ωcm.By setting a range of the electrical resistivity of the electrode member12 as just described, the pair of electrode members 12 and 12effectively performs a function as electrodes inside the pipe where thehigh temperature exhaust gas flows. In the first honeycomb structure 1,the electrical resistivity of the electrode member 12 is preferablylower than the electrical resistivity of the honeycomb structure body11. The electrical resistivity of the electrode member 12 is the valueat 25° C. Also, the electrical resistivity of the electrode member 12 isthe value measured by a four-terminal method.

In each of the electrode members 12 and 12, an electrode terminalprojecting portion 18 for connection with electrical wiring from outsidemay be arranged, respectively. The material of the electrode terminalprojecting portion 18 may be a conductive ceramic or metal. The materialof the electrode terminal projecting portion 18 is preferably the sameas that of the electrode member 12. Also, the electrode terminalprojecting portion 18 and the connector 6 of the outer cylinder 4 arepreferably connected by electrical wiring 7.

(1-2) Urea Spraying Device:

The urea spraying device 2 is preferably a solenoid type, an ultrasonictype, a piezoelectric actuator type, or an atomizer type. By using thesetypes, the urea water solution can be sprayed in mist form. Among thesetypes, use of the solenoid type, the ultrasonic type, or thepiezoelectric actuator type makes it possible to spray the urea watersolution in mist form without use of air. Accordingly, the firsthoneycomb structure 1 does not need to heat even the air used for theurea injection and can reduce an energy amount for heating. Furthermore,a reduction of an injection volume due to no injection air allowsdecreasing a speed at which “the urea water solution in mist form”passes through the honeycomb structure, and thus this ensures having alonger reaction time necessary for hydrolysis. A size (diameter) ofdroplets of the urea water solution sprayed from the urea sprayingdevice 2 is preferably 0.3 mm or less. When the size of droplets islarger than 0.3 mm, the droplets may be less likely to evaporate whenthey receive heat from the first honeycomb structure 1.

A urea spraying device 2 of a solenoid type is a device that sprays aurea water solution in mist form by “vibration of a solenoid” or“forward and backward movement of a piston due to an electric field whena solenoid is used”.

A urea spraying device 2 of an ultrasonic type is a device that sprays aurea water solution in mist form by an ultrasonic vibration.

A urea spraying device 2 of a piezoelectric actuator type is a devicethat sprays a urea water solution in mist form by a vibration of apiezoelectric element.

A urea spraying device 2 of an atomizer type is, for example, a devicethat, while drawing up a fluid by a tube, blows off “the fluid drawn upin an open end at a distal end of this tube” in mist form by air, andsprays this fluid. Also, a urea spraying device 2 of an atomizer typemay be even a device that sprays a fluid in mist form from a pluralityof small open ends formed at a distal end of a nozzle of the device.

In the reducing agent injection device 100 of the embodiment, the ureawater solution is preferably sprayed toward the first end face 13 of thefirst honeycomb structure 1 from the urea spraying device 2. That is, inthe urea spraying device 2, a spraying direction (ejected direction ofdroplets) of the urea water solution preferably faces to the first endface 13 of the first honeycomb structure 1.

(1-3) Urea Hydrolysis Catalyst:

It is preferable that a urea hydrolysis catalyst 40 is provided in thesecond end face 14 side of the first honeycomb structure 1 (honeycombstructure body 11), with a gap from the second end face 14. Thereby,ammonia can be efficiently generated from urea. As the urea hydrolysiscatalyst 40, copper zeolite, aluminum oxide and the like can beincluded.

It is preferable that the urea hydrolysis catalyst 40 is loaded onto ahoneycomb structure (hereinafter, called a honeycomb structure that is acarrier of the urea hydrolysis catalyst 40 as a second honeycombstructure 41.) similar to the first honeycomb structure 1 at itsupstream (urea hydrolysis catalyzer 43). More specifically, a carrierloading the urea hydrolysis catalyst 40 is preferably a honeycombstructure having partition walls defining and forming “a plurality ofcells which is through channels of a fluid and extends from a first endface to a second end face”. Also, in this second honeycomb structure 41,a circumferential wall 47 is arranged outside the partition wall 45. Ina honeycomb structure body 42, the material of the partition wall 45 andthe circumferential wall 47 is preferably ceramic. Particularly, thematerial of the partition wall 45 and the circumferential wall 47 ispreferably mainly composed of “silicon-silicon carbide compositematerial”, “silicon carbide”, and the like. The second honeycombstructure 41 may be configured such that the cell structure and L/D aredifferent from those of the first honeycomb structure 1, consideringcatalyst performance due to permeability of urea and hydrolysis. Also,the second honeycomb structure 41 may not include an electrode member,but may include a pair of electrode members as the first honeycombstructure 1, and configured so as to be electrically heated.

(2) Manufacturing Method of Reducing Agent Injection Device:

(2-1) Manufacturing of First Honeycomb Structure:

When the honeycomb structure is made of ceramic, the manufacturingmethod of the honeycomb structure is preferably the manufacturing methoddescribed as follows. The manufacturing method of the honeycombstructure preferably includes a honeycomb formed body forming process, adried honeycomb body forming process, an unfired electrode providedhoneycomb body forming process, and a honeycomb structure formingprocess.

(2-1-1) Honeycomb Formed Body Forming Process:

In the honeycomb formed body forming process, the honeycomb formed bodyis preferably formed by extrusion of the forming raw material. Theforming raw material is preferably a raw material containing a ceramicraw material and an organic binder. In the forming raw material, asurfactant, a sintering additive, a pore former, water and the likebesides a ceramic raw material and an organic binder are preferablycontained. The forming raw material can be prepared by mixture of theseraw materials.

The ceramic raw material in the forming raw material is “ceramic” or “araw material which becomes ceramic by firing.” The ceramic raw materialbecomes ceramic after firing in both cases. The ceramic raw material inthe forming raw material preferably contains metal silicon and siliconcarbide particles (silicon carbide powder) as main components or siliconcarbide particles (silicon carbide powder) as a main component.Accordingly, the obtained honeycomb structure exhibits electricalconductivity. Metal silicon is also preferably metal silicon particles(metal silicon powder). Also, “containing metal silicon and the siliconcarbide particles as main components” means that a total mass of themetal silicon and silicon carbide particles is 90% by mass or more ofthe whole material (ceramic raw material). Moreover, as componentscontained in the ceramic raw material other than main component, SiO₂,SrCO₃, Al₂O₃, MgCO₃, cordierite and the like can be included.

When silicon carbide is used as the main component of the ceramic rawmaterial, the silicon carbide is sintered by firing. Also, when metalsilicon and silicon carbide particles are used as the main component ofthe ceramic raw material, the silicon carbide as aggregates can bebonded together by firing with metal silicon used as a bonding material.

When silicon carbide particles (silicon carbide powder) and metalsilicon particles (metal silicon powder) are used as the ceramic rawmaterial, the mass of the metal silicon particles is preferably from 10%by mass to 40% by mass with respect to the total of the mass of thesilicon carbide particles and the mass of the metal silicon particles.The average particle diameter of the silicon carbide particles ispreferably from 10 μm to 50 μm, and further preferably from 15 μm to 35μm. The average particle diameter of the metal silicon particles ispreferably from 0.1 μm to 20 μm, and further preferably from 1 μm to 10μm. The average particle diameters of the silicon carbide particles andmetal silicon particles are values measured by a laser diffractionmethod.

As the organic binder, methyl cellulose, glycerin, hydroxypropyl methylcellulose and the like can be included. As the organic binder, one kindof organic binder may be used, and plural kinds of organic binders maybe used. The content of the organic binder is preferably from 5 parts bymass to 10 parts by mass when the total mass of the ceramic raw materialis 100 parts by mass.

As the surfactant, ethylene glycol, dextrin and the like can be used. Asthe surfactant, one kind of surfactant may be used, and plural kinds ofsurfactants may be used. The content of the surfactant is preferablyfrom 0.1 parts by mass to 2.0 parts by mass when the total mass of theceramic raw material is 100 parts by mass.

As the sintering additive, SiO₂, SrCO₃, Al₂O₃, MgCO₃, cordierite and thelike can be used. As the sintering additive, one kind of sinteringadditive may be used, and plural kinds of sintering additives may beused. The content of the sintering additive is preferably from 0.1 partsby mass to 3 parts by mass when the total mass of the ceramic rawmaterial is 100 parts by mass.

The pore former is not especially limited as long as it forms poresafter firing, and, for example, graphite, starch, a foamable resin, awater absorbable resin, silica gel and the like can be included as thepore former. As the pore former, one kind of pore former may be used,and plural kinds of pore formers may be used. The content of the poreformer is preferably from 0.5 parts by mass to 10 parts by mass when thetotal mass of the ceramic raw material is 100 parts by mass.

The content of water is preferably 20 parts by mass to 60 parts by masswhen the total mass of the ceramic raw material is 100 parts by mass.

When extruding the forming raw material, first, the forming raw materialis preferably kneaded to form a kneaded material. Next, the kneadedmaterial is preferably extruded to form the honeycomb formed body. Thehoneycomb formed body has porous partition walls defining and forming “aplurality of cells which is through channels of a fluid and extends froma first end face being an end face on an inflow side of the fluid to asecond end face being an end face on an outflow side of the fluid”. Thehoneycomb formed body formed to have a circumferential wall positionedin an outermost circumference is also a preferable aspect. The partitionwall of the honeycomb formed body is an undried and unfired partitionwall.

(2-1-2) Dried Honeycomb Body Forming Process:

The dried honeycomb body forming process is preferably a process to drythe obtained honeycomb formed body and form a dried honeycomb body. Adrying condition is not especially limited, and a known condition can beused. It is preferable, for example, to dry for 0.5 hours to 5 hours at80° C. to 120° C.

(2-1-3) Unfired Electrode Provided Honeycomb Body Forming Process:

In the unfired electrode provided honeycomb body forming process, slurryfor electrode formation containing the ceramic raw material and water ispreferably applied over the side surface of the dried honeycomb body.Thereafter, the slurry for electrode formation is preferably dried toform an unfired electrode and form an unfired electrode providedhoneycomb body.

In the unfired electrode provided honeycomb body, the unfired electrodehaving rectangular shape with a wider width, which extends to the cellextending direction in a band shape and expands also in acircumferential direction, is preferably formed to the dried honeycombbody. The circumferential direction is a direction along the sidesurface of the dried honeycomb body in a cross section perpendicular tothe cell extending direction.

The slurry for electrode formation used in the unfired electrodeprovided honeycomb body forming process contains the ceramic rawmaterial and water, and preferably contains the surfactant, the poreformer, water and the like, besides these materials.

As the ceramic raw material, it is preferable to use the ceramic rawmaterial used when the honeycomb formed body is formed. For example,when the main components of the ceramic raw material used when thehoneycomb formed body is formed are silicon carbide particles and metalsilicon, the silicon carbide particles and metal silicon are preferablyused also as the ceramic raw material of the slurry for electrodeformation.

The method to apply the slurry for electrode formation over the sidesurface of the dried honeycomb body is not especially limited. Forexample, the method to apply by use of a brush or a printing techniquecan be employed.

Viscosity of the slurry for electrode formation is preferably 500 Pa·sor less, and further preferably 10 Pa·s to 200 Pa·s, at 20° C. Theviscosity exceeding 500 Pa·s may make it difficult to apply the slurryfor electrode formation over the side surface of the dried honeycombbody.

After application of the slurry for electrode formation to the driedhoneycomb body, the slurry for electrode formation is preferably driedto form the unfired electrode (unfired electrode provided honeycombbody). The drying temperature is preferably 80° C. to 120° C. The dryingtime is preferably 0.1 hours to 5 hours.

(2-1-4) Honeycomb Structure Forming Process:

The honeycomb structure forming process is a process to form a honeycombstructure by firing the unfired electrode provided honeycomb body.

The firing condition can be appropriately determined based on theceramic raw material used for manufacturing of the honeycomb formed bodyand the kind of the ceramic raw material used for the slurry forelectrode formation.

Moreover, after the unfired electrode provided honeycomb body is dried,before firing, calcination is preferably performed for reducing thebinder and the like. The calcination is preferably performed for 0.5hours to 20 hours at 400° C. to 500° C. under the air atmosphere.

(2-2) Manufacturing of Reducing Agent Injection Device:

The reducing agent injection device 100 is preferably manufactured asfollows: a connector connecting electrical wiring from outside ismounted on the outer cylinder 4, and then the honeycomb structure andthe urea spraying device 2 are housed and secured in the outer cylinder4.

The outer cylinder 4 is preferably formed by forming a material, such asstainless steel, in a tubular shape. The honeycomb structure ispreferably secured inside the outer cylinder 4 by the insulationsupporting portion. Also, when there is a portion (space) where theinsulation supporting portion between the honeycomb structure and theouter cylinder 4 is not arranged, it is preferable to fill it with aninsulating member.

(2-3) Manufacturing of Urea Hydrolysis Catalyzer:

A second honeycomb structure 41 can be manufactured in the same manneras the first honeycomb structure 1 described above.

Next, a urea hydrolysis catalyst 40 is loaded onto the second honeycombstructure 41 to manufacture a urea hydrolysis catalyzer 43. As the ureahydrolysis catalyst 40, for example, aluminum oxide can be used. As themethod of loading the urea hydrolysis catalyst 40 onto a partition wall45 of the second honeycomb structure 41, for example, the secondhoneycomb structure 41 is immersed in a container in which slurry of theurea hydrolysis catalyst 40 is stored. The viscosity of the slurry ofthe urea hydrolysis catalyst 40, the particle size of the contained ureahydrolysis catalyst 40 and the like are adjusted, whereby the catalystcan be loaded onto not only the surface of the partition wall 45, butalso the inside of pores of the partition wall 45, and further, theamount of the loaded catalyst can be also adjusted. Also, aspiration ofslurry is performed a plurality of times, whereby the amount of theloaded catalyst can be also adjusted.

(3) Method for Using Reducing Agent Injection Device:

The following describes a method for using the reducing agent injectiondevice 100 (see FIG. 1) of the embodiment.

The reducing agent injection device 100, when a urea water solution issupplied, can hydrolyze urea in the supplied urea water solution, andinject ammonia. The urea water solution is a raw material for generationof ammonia. Further, specifically, after energizing the first honeycombstructure 1 to raise its temperature (heating) and supplying the ureawater solution to the urea spraying device 2, the urea water solution inmist form is preferably sprayed into the urea spraying space 3 from theurea spraying device 2. When the urea water solution is sprayed from theurea spraying device 2, the urea water solution is preferably sprayedtoward the first end face 13 of the first honeycomb structure 1. Then,the urea water solution in mist form (the urea water solution a sprayedfrom the urea spraying device 2) sprayed into the urea spraying space 3is heated by the first honeycomb structure 1 and evaporates. Because thepressure inside the urea spraying space 3 increases due to evaporationof the urea water solution, urea and water enter into the cell 16 of thefirst honeycomb structure 1 from the first end face 13. The ureasupplied into the cell 16 is hydrolyzed by the temperature of the firstheated honeycomb structure 1, and ammonia b is generated.

The supply amount of the urea water solution is preferably 1.0 to 2.0 interms of an equivalence ratio with respect to the amount of nitrogenoxides contained in the exhaust gas. When the supply amount of the ureawater solution is 1.0 or less in terms of the equivalence ratio, theamount of nitrogen oxide discharged without being purified may increase.When the supply amount of the urea water solution exceeds 2.0 in termsof the equivalence ratio, it may be more likely that the exhaust gas isdischarged with ammonia mixed in the exhaust gas.

The urea water solution is preferably the urea water solution of 10% bymass to 40% by mass. When the value is lower than 10% by mass, because alarge amount of urea water is required to be injected for NO_(X)reduction, the amount of electric power used in a honeycomb heater mayincrease. When the value is higher than 40% by mass, there is a concernthat urea solidifies in cold region. In the most preferable example,AdBlue (32.5% by mass urea water solution) widely distributed on themarket is used.

The temperature of the first honeycomb structure 1 is preferably 160° C.or more, further preferably 160° C. to 600° C., and especiallypreferably 160° C. to 400° C. When the temperature is lower than 160°C., it may be difficult to hydrolyze urea. When the temperature ishigher than 600° C., ammonia is burnt, and ammonia may not be suppliedto the exhaust pipe. Also, the temperature of the first honeycombstructure 1 is preferably 360° C. or more in that a sulfur compound,such as ammonium hydrogen sulfate and ammonium sulfate, which depositsin the reducing agent injection device 100 can be removed.

The maximum voltage to be applied to the first honeycomb structure 1 ispreferably 12 V to 200 V, further preferably 12 V to 100 V, andespecially preferably 12 V to 48 V. When the maximum voltage is lowerthan 12 V, it may be difficult to raise the temperature of the firsthoneycomb structure 1. The maximum voltage higher than 200 V requires amore expensive voltage booster and is not preferable.

(4) Exhaust Gas Treatment Device:

One embodiment (exhaust gas treatment device 200) of the exhaust gastreatment device of the present invention includes, as shown in FIG. 3,an exhaust pipe 51, a reducing agent injection device 100, an SCRcatalyst 52 arranged on “the downstream side of the exhaust pipe 51 withrespect to the position where ammonia is injected.” The reducing agentinjection device 100 injects ammonia into the exhaust pipe 51. Theexhaust pipe 51 is a pipe that flows “an exhaust gas c containingNO_(X).”

The exhaust pipe 51 is a pipe passing the exhaust gas (the exhaust gas ccontaining NO_(X)) discharged from various kinds of engines, and theexhaust gas and ammonia are mixed in the exhaust pipe 51. The size ofthe exhaust pipe 51 is not especially limited and can be appropriatelydetermined in accordance with an exhaust system of an engine and thelike where the exhaust gas treatment device 200 of the embodiment ismounted. Though the length in the gas flowing direction in the exhaustpipe 51 is not especially limited, it is preferable for the length tomake a distance between the reducing agent injection device 100 and theSCR catalyst 52 an appropriate distance.

Though the material of the exhaust pipe 51 is not especially limited, amaterial where corrosion by the exhaust gas is less likely to occur ispreferable. As the material of the exhaust pipe 51, for example,stainless steel and the like are preferable.

The reducing agent injection device 100 is a reducing agent injectiondevice of the present invention. The reducing agent injection device 100is mounted to the exhaust pipe 51 and injects ammonia into the exhaustpipe 51. By injection of ammonia into the exhaust pipe 51 from thereducing agent injection device 100, a mixed gas d of ammonia and theexhaust gas is generated in the exhaust pipe 51.

The exhaust gas treatment device 200 of the embodiment includes the SCRcatalyst 52 arranged on “the downstream side of the exhaust pipe 51 withrespect to the position where ammonia is injected.” The SCR catalyst ispreferably arranged on the downstream side of the exhaust pipe 51 in astate of catalyzer (SCR catalyst loaded onto the ceramic honeycombstructure).

As the SCR catalyst 52, specifically, a vanadium-based catalyst, azeolite-based catalyst and the like can be included.

When the SCR catalyst 52 is used as a catalyzer 53 loaded onto thehoneycomb structure, the catalyzer 53 is housed in a storing container54, and the storing container 54 is preferably mounted on the downstreamside of the exhaust pipe 51.

The honeycomb structure loading the SCR catalyst 52 is not especiallylimited, and a honeycomb structure known as “a ceramic honeycombstructure loading an SCR catalyst” can be used.

In an upstream side of the exhaust pipe 51, a filter for trappingparticulate matter in the exhaust gas is preferably arranged. As thefilter for trapping a particulate matter, for example, ahoneycomb-shaped ceramic diesel particulate filter (DPF) 55 can beincluded. Also, in the upstream side of the exhaust pipe 51, anoxidation catalyst 56 for removing hydrocarbon and carbon monoxide inthe exhaust gas is preferably arranged. The oxidation catalyst ispreferably in a state of being loaded onto the ceramic honeycombstructure (oxidation catalyzer). As the oxidation catalyst, noble metalssuch as platinum (Pt), palladium (Pd), and rhodium (Rh) are suitablyused.

On the downstream side of the SCR catalyst 52, an ammonia removalcatalyst (oxidation catalyst) for removing ammonia is preferablyarranged. This prevents ammonia from being discharged outside when extraammonia not used for removal of NO_(X) in the exhaust gas flows on thedownstream side. As the oxidation catalyst, noble metals such asplatinum (Pt), palladium (Pd), and rhodium (Rh) are suitably used.

(5) Exhaust Gas Treatment Method:

One embodiment of an exhaust gas treatment method of the presentinvention is a method that flows the exhaust gas c into the exhaust pipe51, injects the ammonia b into the exhaust gas c, and performs areduction treatment of the mixed gas by the SCR catalyst 52, by usingthe one embodiment (exhaust gas treatment device 200) of the presentinvention shown in FIG. 3. This allows an exhaust gas e after NO_(X)removal to be obtained. The above-described exhaust gas c containsNO_(X). The above-described mixed gas is “the exhaust gas with ammoniabeing mixed,” and is the mixed gas d of ammonia and the exhaust gas. Theammonia b is injected by the reducing agent injection device 100.

An injection amount of ammonia injected from the reducing agentinjection device 100 is preferably 1.0 to 2.0 in terms of theequivalence ratio with respect to the amount of nitrogen oxide containedin the exhaust gas. When the injection amount of ammonia is less than1.0 in terms of the equivalence ratio, the amount of nitrogen oxidedischarged without being purified may increase. When the injectionamount of ammonia exceeds 2.0 in terms of the equivalence ratio, it maybe more likely that the exhaust gas is discharged with ammonia mixed inthe exhaust gas.

The spraying amount of the urea water solution and the temperature(applied voltage) of the first honeycomb structure 1 are preferablycontrolled by the electronic control device. Preferably, the temperatureof the first honeycomb structure is calculated from the resistance valueof the honeycomb structure and is controlled such that the calculatedtemperature becomes desired temperature.

EXAMPLES

The following describes the present invention more specifically withexamples, but the present invention is not limited to these examples.

Example 1

A reducing agent injection device 100 as shown in FIG. 1 wasmanufactured. It is specifically described as follows. First, a firsthoneycomb structure 1 was prepared.

The silicon carbide (SiC) powder and metal silicon (Si) powder weremixed in a mass ratio of 70:30 to prepare a ceramic raw material. Then,hydroxypropyl methyl cellulose as a binder and a water absorbable resinas a pore former were added to the ceramic raw material, and water wasadded together to prepare a forming raw material. Then, the forming rawmaterial was kneaded by a vacuum pugmill to form a round pillar-shapedkneaded material. The content of the binder was 7 parts by mass when theceramic raw material was 100 parts by mass. The content of the poreformer was 3 parts by mass when the ceramic raw material was 100 partsby mass. The content of water was 42 parts by mass when the ceramic rawmaterial was 100 parts by mass. The average particle diameter of thesilicon carbide powder was 20 μm, and the average particle diameter ofthe metal silicon powder was 6 μm. The average particle diameter of thepore former was 20 μm. The average particle diameters of the siliconcarbide, the metal silicon and the pore former were the values measuredby laser diffraction method.

The obtained round pillar-shaped kneaded material was formed using anextruder to obtain a square pillar-shaped (a pillar shape in which crosssection perpendicular to the cell extending direction is square)honeycomb formed body. After the obtained honeycomb formed body wasdried by high frequency dielectric heating, the obtained honeycombformed body was dried at 120° C. for 2 hours by use of a hot-air dryingmachine, and both end faces were cut as much as predetermined amounts.

Next, the silicon carbide (SiC) powder and metal silicon (Si) powderwere mixed in the mass ratio of 60:40 to prepare the ceramic rawmaterial for the electrode member. Then, hydroxypropyl methyl celluloseas the binder, glycerin as a moisturizing agent, and a surfactant as adispersing agent were added to the ceramic raw material for theelectrode member, and water was added together to mix. The mixture waskneaded to prepare an electrode member forming raw material.

Next, the electrode member forming raw material was applied in a bandshape over two parallel surfaces in the side surfaces of the driedhoneycomb formed body. The electrode member forming raw material wasapplied in a band shape over one side surface among “the side surfaces(four side surfaces) having four planes” of the dried honeycomb formedbody, and was also applied in a band shape over one side surfaceparallel to this “applied side surface.” The shape (circumference shape)of the electrode member forming raw material applied over the sidesurface of the honeycomb formed body was a rectangular shape.

Next, the electrode member forming raw material applied to the honeycombformed body was dried. The drying condition was 70° C.

Next, by using the same material as an electrode forming material, anelectrode terminal projecting portion forming member was obtained.

Next, each of two electrode terminal projecting portion forming memberswas laminated to the respective portions, where the electrode memberforming raw material was applied, of two places of the honeycomb formedbody, respectively. Afterwards, the honeycomb formed body was degreased,fired, and further underwent oxidation treatment to obtain the honeycombstructure. The degreasing condition was set at 550° C. for 3 hours. Thefiring condition was set at 1,450° C. for 2 hours, under the argonatmosphere. The oxidation treatment condition was set at 1,300° C. for 1hour.

The thickness of the partition walls of the obtained first honeycombstructure 1 was 0.152 mm, and the cell pitch was 1.11 mm. The surfacearea per unit volume of the honeycomb structure body 11 was 31.1cm²/cm³. The shape of the first honeycomb structure 1 was a pillar shapewith a square bottom surface. One side of the bottom surface of thefirst honeycomb structure 1 was 35 mm. The length in the cell extendingdirection of the first honeycomb structure 1 was 35 mm. The electricalresistivity of the electrode member was 0.1) cm, and the electricalresistivity of the honeycomb structure body 11 was 1.4 Ωcm. A pluggingportion was not formed in the first honeycomb structure 1.

An outer cylinder 4 was formed with a stainless steel. In the outercircumference of the outer cylinder 4, two connectors for electricalwiring were mounted. The first honeycomb structure 1 was inserted intothe outer cylinder 4 and secured by an insulation supporting member.Then, the electrode terminal projecting portions of the first honeycombstructure 1 were connected to the connectors in the outer cylinder 4 byelectrical wiring. A urea spraying device 2 of a solenoid type wasmounted inside the inlet side end portion of the outer cylinder 4 toobtain a reducing agent injection device 100.

Examples 2 to 10, Comparative Examples 1 to 3

As to Examples 2 to 10, and Comparative Examples 1 to 3, a firsthoneycomb structure 1 was also prepared in the same manner as in Example1, by changing length L in the cell 16 extending direction of thehoneycomb structure body 11 and diameter D of the cross sectionperpendicular to the cell 16 extending direction. The size is shown inTable 1.

Furthermore, as to Examples 5 to 10, a second honeycomb structure 41 wasprepared in the same manner as the first honeycomb structure 1. Copperzeolite was loaded onto the second honeycomb structure 41 as a ureahydrolysis catalyst 40. An electrode member was not formed in the secondhoneycomb structure 41.

A reducing agent injection device 100 as shown in FIG. 1 was prepared,and the generation amount of ammonia was measured. Examples 1 to 4, andComparative Examples 1 to 3 were not provided with the urea hydrolysiscatalyst 40. On the other hand, Examples 5 to 10 were provided with theurea hydrolysis catalyst 40 in the downstream of the honeycombstructure.

For measurement of the generation amount of ammonia, specifically, NH₃concentration in an injection port 23 of the reducing agent injectiondevice 100 was measured using an FTIR gas analyzer. An experiment wasperformed for 30 minutes while adding urea in an amount listed in Table1, then breakage and generation of deposit were examined. The breakageof a heater (first honeycomb structure 1) was determined by the presenceor absence of crack, by visual observation. As to the generation ofdeposit, the first end face 13 of the first honeycomb structure 1 wasvisually observed, and judged the presence or absence of deposit. Also,as to the inside of the first honeycomb structure 1, the presence orabsence of deposit was determined by X-ray CT (Computed Tomography)observation.

The experiment result is shown in Table 1. The case where the heater(first honeycomb structure 1) is not broken is shown by A, and the casewhere the heater is broken is shown by B. In addition, the case wheredeposit was not generated is shown by A, and the case where deposit wasgenerated is shown by B.

TABLE 1 Result Amount of Heater size Generation urea added D L Latterhydrolysis catalyst Electric power Breakage of amount of (g/min) (mm)(mm) L/D D(mm) × L(mm) (W) heater Deposit NH₃ (ppm) Comparative Example1 3 35 45 1.3 Not used 400 A B — Comparative Example 2 3 35 45 1.3 Notused 450 B — — Example 1 3 35 35 1.0 Not used 450 A A 640 Example 2 3 3525 0.7 Not used 450 A A 620 Example 3 3 35 25 0.7 Not used 400 A A 610Example 4 3 35 20 0.6 Not used 400 A A 600 Comparative Example 3 3 35 150.4 Not used 400 B — — Example 5 3 35 25 0.7 Used 35 × 25 450 A A 660Example 6 3 35 25 0.7 Used 35 × 25 400 A A 660 Example 7 3 35 25 0.7Used 35 × 15 450 A A 660 Example 8 3 35 25 0.7 Used 35 × 15 400 A A 660Example 9 3 35 20 0.6 Used 35 × 25 400 A A 660 Example 10 3 35 20 0.6Used 35 × 15 400 A A 660

In Comparative Example 1, L/D was large, thus the temperature was notsufficient, and deposit was generated. In Comparative Example 2, L/D waslarge, thus, when electric power was increased, the temperaturedistribution expanded, and the heater was broken. In Comparative Example3, L/D was too small, and strength was not sufficient.

On the other hand, when L/D was within the range of 0.5 to 1.2, theheater was not broken, and urea deposit was not also generated. Inaddition, when provided with the urea hydrolysis catalyst 40 likeExamples 5 to 10, the generation amount of ammonia was increased.

The reducing agent injection device and exhaust gas treatment device ofthe present invention can be suitably used to purify nitrogen oxides(NO_(X)) in an exhaust gas discharged from various kinds of engines andthe like.

DESCRIPTION OF REFERENCE NUMERALS

-   -   1 first honeycomb structure    -   2 urea spraying device    -   3 urea spraying space    -   4 outer cylinder    -   5 insulation supporting portion    -   6 connector    -   7 electrical wiring    -   11 honeycomb structure body    -   12 electrode member    -   13 first end face    -   14 second end face    -   15 partition wall    -   16 cell    -   17 circumferential wall    -   18 electrode terminal projecting portion    -   21 inlet side end portion (of outer cylinder)    -   22 outlet side end portion (of outer cylinder)    -   23 injection port    -   40 urea hydrolysis catalyst    -   41 second honeycomb structure    -   42 honeycomb structure body    -   43 urea hydrolysis catalyzer    -   45 partition wall    -   47 circumferential wall    -   51 exhaust pipe    -   52 SCR catalyst    -   53 catalyzer    -   54 storing container    -   55 DPF    -   56 oxidation catalyst    -   100 reducing agent injection device    -   200 exhaust gas treatment device    -   a urea water solution sprayed from urea spraying device    -   b ammonia    -   c exhaust gas    -   d mixed gas of ammonia and exhaust gas    -   e exhaust gas after removal of NO_(X)

What is claimed is:
 1. A reducing agent injection device, comprising: afirst honeycomb structure that has a pillar-shaped honeycomb structurebody having partition walls defining and forming a plurality of cellswhich is through channels of a fluid and extends from a first end facebeing an end face on an inflow side of the fluid to a second end facebeing an end face on an outflow side of the fluid, and that has at leasta pair of electrode members arranged in a side surface of the honeycombstructure body; and a urea spraying device that sprays a urea watersolution in mist form, wherein each of the pair of electrode members isformed in a band shape extending to a cell extending direction of thehoneycomb structure body, and one electrode member of the pair ofelectrode members is arranged on an opposite side of the other electrodemember of the pair of electrode members with respect to a center of thehoneycomb structure body sandwiched by the pair of electrode members, ina cross section perpendicular to the cell extending direction, the ratioL/D of length L in the cell extending direction of the honeycombstructure body to diameter D of the cross section perpendicular to thecell extending direction is 0.5 to 1.2, and the urea water solutionsprayed from the urea spraying device is supplied into the cells fromthe first end face of the honeycomb structure body, and urea in the ureawater solution supplied into the cells is heated and hydrolyzed in theelectrically heated honeycomb structure body to generate ammonia, andthe ammonia is discharged outside the honeycomb structure body from thesecond end face and is injected outside.
 2. The reducing agent injectiondevice according to claim 1, wherein a urea hydrolysis catalyst isprovided in the second end face side of the honeycomb structure body,with a gap from the second end face.
 3. An exhaust gas treatment device,comprising: an exhaust pipe that flows an exhaust gas containing NO_(X);the reducing agent injection device according to claim 1 that injectsammonia into the exhaust pipe; and an SCR catalyst arranged on adownstream side of the exhaust pipe with respect to a position where theammonia is injected.